Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section.
An x-ray system typically includes an x-ray tube and an imager (or detector). The power and signals for the x-ray tube can be provided by a high voltage generator. The x-ray tube emits radiation, such as x-rays, toward an object. The object is positioned between the x-ray tube and the imager. The radiation typically passes through the object and impinges on the imager. As radiation passes through the object, internal structures of the object cause attenuation in the radiation received at the imager. The imager then generates data based on the detected radiation, and the system translates or reconstructs the radiation attenuations into an image with spatial variances, which may be used to evaluate the internal structure of the object, such as a patient in a medical imaging procedure or an inanimate object in an inspection scan.
The x-ray tube includes a cathode and an anode. X-rays are produced in x-ray tubes by applying an electrical current to a filament positioned within the cathode to cause electrons to be emitted from the cathode by thermionic emission. In a vacuum, the electrons accelerate towards and then impinge upon the anode due to the voltage difference between the cathode and the anode. When the electrons collide with a target on the anode, some of the energy is emitted as x-rays, and the majority of the energy is released as heat. The area on the anode in which the electrons collide is generally known as the focal spot, and the emitted x-rays can have a central ray (i.e., central ray beam, central x-ray beam, center ray beam, center x-ray beam, or center ray) emanating from the focal spot, and the central ray represents a point area in x-ray beam with a high intensity. A focal spot size can be determined by an x-ray system design, an x-ray tube structure, a tube voltage (e.g., with units of kilovolts [kV]), and a tube current (e.g., with units of milliamps [mA]). Because of high temperatures generated when the electron beam strikes the target, specifically the focal spot, the anode can include features to distribute the heat generated at the focal spot on the target, such as rotating a disc-shaped anode target at a high rotational speed. A rotating anode typically includes the disc-shaped anode target, which is rotated by an induction motor via a bearing assembly.
The radiation imager (e.g., x-ray detector, x-ray imager, or radiation detector) can include a conversion element that converts an incoming radiation beam into electrical signals, which can be used to generate data about the radiation beam, which in turn can be used to characterize an object being inspected (e.g., the patient or inanimate object). In one example, the conversion element includes a scintillator that converts a radiation beam into light, and a sensor that generates electrical signals in response to the light. The imager can also include processing circuitry that processes the electrical signals to generate data about the radiation beam.
The x-ray tube and radiation imager can be components in an x-ray system, such as a computed tomography (CT) system or scanner, which includes a gantry that rotates both the x-ray tube and the imager to generate various images of the object at different angles. The CT scanner may also include a collimator to limit the exposure area of the emitted x-rays. A collimator is a device that narrows a beam of particles or waves (e.g., x-rays) to cause the directions of the beam to become more aligned in a specific direction or to cause the spatial cross section of the beam to become smaller. The x-ray tube, the radiation imager, the collimator, and the generator can be separate components that are attached to the gantry.
Conventionally, to ensure image quality, good accuracy, and high resolution, the x-ray tube is mechanically aligned to the gantry and the collimator so the central ray of the x-ray tube is centered on a specified location on the detector (e.g., center point on the detector). Mechanical alignment of the x-ray tube on the gantry can be time consuming, cumbersome, and iterative, especially for fine tune adjustments (e.g., sub millimeter range). For example, to achieve the correct positioning of the x-ray tube, a series of images can be taken and the central ray representing the focal spot location can be determined from the images. Subsequently, the x-ray tube can be adjusted and another series of images can be taken to determine the focal spot position (or central ray). The x-ray tube is adjusted and the sequence is repeated again until a satisfactory alignment of the x-ray tube relative to the detector is achieved.
The technology (systems, devices, and methods) described herein provides alternatives to mechanical alignment, especially for fine tune adjustments of the focal spot position, and thus the central ray.